Prosthetic devices which are implanted for replacement of joints are well known. Such implants take the place of the body's own joints which fail, such as may be required for patients suffering from rheumatism, degenerative or traumatic arthritis, including osteoarthritis. A number of problems are associated with joint replacement. The joint should function in a manner which simulates the natural joint, providing substantially the same degree of motion.
The ankle joint, or joint between the leg bones, tibia and fibula, and the talus, are frequently a source of osteo or rheumatoid arthritis. Typically, sufferers of rheumatoid and osteoarthritis at the ankle joint have been generally limited to a procedure called fusing. In a fusing procedure, the tibia and talus are fused or secured together to reduce the patient's pain and improve mobility. Clearly, the use of fusing does not provide the same degree of motion as a natural ankle joint.
For example, for ankle replacements, the joint should supply at least the same degree of motion as is required for walking. In addition, the joint should not occupy more space in the body than the natural joint. Problems arise in connection with the replacement joint to bone and tissue. The joint should also be easy to implant as possible so that intricate operations are not required, thus reducing the chance of complications. The joints must have sufficient strength and durability to withstand the weight and stresses which are applied.
Ankle joints pose additional problems due to the weight supported and range of motion required for walking. Attachment of the tibia, which extends substantially vertically is difficult, as portions of the fibula may also be removed for implants. Matching the pivot point of the joint is critical, as misalignment can lead to difficulty in walking and other motions, which may cause the patient considerable pain.
The durability of a replacement joint is also important, as the ankle experiences high stresses during walking, running, and jumping, as well as fatigue over time. These stresses may crack or fracture ankle components of replacement joints, which absorb a substantial amount of the pressures during the aforementioned activities.
A particularly successful ankle implant for use in total ankle arthroplasty is disclosed in U.S. Pat. No. 5,326,365 to Alvine, and assigned to the same assignee as the instant application. U.S. Pat. No. 5,326,365 is hereby incorporated in its entirety by reference.
The total ankle implant, as disclosed in U.S. Pat. No. 5,326,365, is marketed by DePuy Orthopaedics, Inc. under the name Agility™ Ankle. The current surgical technique for the Agility™ Ankle and the associated instrument system for the Agility™ Ankle utilizes a reciprocating or oscillating saw and a freehand method for forming the talar component keel slot.
The utilization of a freehand method is very dependent upon surgeon skill and may provide for lack of accuracy and repeatability in the forming of the slot. For example, the slot may be too deep, too far posterior or too wide for the required geometry of the talar fin. The results of an inaccurate cut include disruption of the anterior and posterior cortex where sufficient bone support occurs. An inaccurate cut may result in the need for excess bone graft to fill the voids from the inaccurate cut. If the slot is cut too deep, talar fractures may occur over time based upon the type of activities of the patient.
It can be seen that an instrumentation system and surgical procedure is needed which is able to increase the precision, accuracy, and repeatability of forming the talar keel slot with the additional benefit of decreased operating room time for the surgeon.